A conventional light-emitting diode (LED) system of which color temperature of emitted light is controllable includes an LED module, and a controller coupled to the LED module to control the color temperature of light emitted by the LED module. The controller is provided with a button. A user may cyclically change the color temperature of light emitted by the LED module by repeatedly pressing the button in order for the LED module to emit light with an intended color temperature based on the number of times the button is pressed. In this situation, each time the button is pressed, the color temperature changes accordingly. However, the color-temperature variations that occur before the intended color temperature is reached may be quite bothersome or uncomfortable to the user.